The present invention relates generally to shaft couplings and more particularly to a shaft coupling for transmitting a torque force from one shaft to another. The problem of how to couple one shaft to another for transmitting a torque force is a long-standing one. This has particularly been a problem in the farming community wherein the power take-off of an agricultural tractor frequently needs to be connected and disconnected to utilize one implement and then another. This problem has been solved in the past in one degree or another, and one of the most commercially successful of these solutions is a connection of the type disclosed in U.S. Pat. No. 2,448,278, which was patented in 1948.
In U.S. Pat. No. 2,448,278 a pin is biased to one position within a housing so that it will contact one spline of a power take-off to thereby hold the coupling together. In another position of the pin, it is moved so that it does not block or contact any of the splines and thereby allows the housing to be removed from the power take-off shaft.
Since the time that the coupling disclosed in U.S. Pat. No. 2,448,278 was developed, the horsepower rating of typical agricultural tractors has continued to increase. Because of the very high torque which can be developed from the power take-offs of modern day agricultural tractors, it is desirable that the coupling be held at more than one point and on more than one spline.
Additionally, it is highly desirable to have a coupling which has no external projections thereon, to prevent such projections from catching a tractor operator's clothes or body limbs. It is for this reason that many various types of shields and guards have been developed to be placed around the couplings of the type shown in U.S. Pat. No. 2,448,278. It has been found, however, that these shields are often removed, or not used at all, because of the inconvenience they cause when a person is trying to get the coupling on and off of a tractor power take-off shaft. Consequently, if the coupling could be designed to be smooth and circular, it would pose less of a safety hazard, whether the safety shield was on or off.
While certain couplers have been developed to avoid these projections, for example as shown in U.S. Pat. No. 3,480,310, there has not been a commercial coupling having the positive coupling to each and every spline which is highly desirable for the high horsepower tractors of today. Furthermore, in trying to eliminate the projections, some of the couplings developed have become unduly complicated and uneconomical to manufacture.
A French Pat. No. 1,102,886, patented in 1955 discloses a design for locking on all of the splines of a power take-off shaft but it has not become a commercial success, at least not in this country, presumably because of its somewhat complicated structure for positioning and biasing the locking splines.